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CULTURE CONNECTION

Physostegia virginiana, with its upright habit, is pri-marily used as a backdrop in landscapes or for late-

season production in large con-tainer sizes. However, thanks to the breeding eff orts of Benary Seed and its introduction of ‘Crystal Peak White’ to the industry, phys-ostegia now off ers great versatility to commercial growers and land-scape settings.

‘Crystal Peak White’ is a fi rst-year-fl owering perennial with a compact, well-branched habit that produces numerous fl ower spikes that last throughout the summer. Th e most notable diff erence between ‘Crystal Peak White’ and other cultivars is its compact size; it reaches only 16 inches in full bloom; many cultivars com-monly grow to at least 36 inches. It also off ers bright-white fl ower spikes that do not fade or brown as they age, as

many of the existing cultivars do. Based on its attributes and performance, phys-ostegia ‘Crystal Peak White’ received the prestigious Fleurose-

lect Gold Medal this year, awarded for excellence in breeding and beauty.

‘Crystal Peak White’ performs well across a wide portion of the United States, throughout USDA Hardiness Zones 2 to 9 and AHS Heat Zones 4 to 8. It prefers full sun, but it performs best in the South with some partial shade. Its common name, Obedient Plant, is derived from the fl owers’ ability to be manu-ally moved on the stem and remain as arranged. ‘Crystal Peak White’ can be used as a border plant to attract hummingbirds, in mass plantings or as cut fl owers. With its compact plant habit, this cultivar is well suited for container production or as a fi ller in mixed-combination planters.

Propagation Physostegia ‘Crystal Peak White’

is propagated from seed. Sow two to three seeds per cell. Cover the seed lightly with germination mix or ver-miculite after sowing to help main-tain a suitable environment around the seed during germination. Moisten the seed fl ats and move them into a warm environment where tempera-tures can be maintained at 66-72° F for germination. Consider ger-minating physostegia in a chamber where uniform moisture levels and temperatures can be maintained.

Seedlings typically emerge within 10 to 16 days of sowing. Reduce moisture levels after germination and allow the growing medium to dry out slightly before watering. Following germination, they can be grown at

slightly lower temperatures (60-64° F) until they reach a transplantable size. Fertilizers can be applied once the true leaves are present, applying 150-ppm nitrogen every third irri-gation or 75 ppm with every irriga-tion, using a balanced, water-soluble source. It takes six to seven weeks for plugs grown in 288-cell trays to reach a transplantable size when they are grown at 65° F.

ProductionPhysostegia is easy to grow and

performs best when grown in a moist, well-drained medium with a slightly acidic pH of 5.5-6.2. When planting into gallon or smaller containers, use one 50- to 72-cell sized plug per container; when larger container sizes are being grown, plant multiple plugs per container to produce fuller containers. ‘Crystal Peak White’ per-forms best under “average” watering regimes. When irrigation is needed, water thoroughly and allow the medium to dry between waterings.

Although ‘Crystal Peak White’ is bred for fi rst-year fl owering, many growers plant them during the late summer prior to the intended date

By Paul Pilon

The fl owers of “obedient plant” can be moved manually along the stem and keep their place.

Physostegia virginiana ‘Crystal Peak White’

PERENNIAL SOLUTIONS

This fi rst-year-fl owering perennial produces numerous bright

white spikes that are sure to get attention in the garden

of sale. Planting physostegia in this manner allows them to bulk up, produce more fl owers per plant, and bloom more uniformly compared to when they are planted and grown for sales in the same growing season.

Physostegia are moderate feeders and perform best under a constant

liquid fertilization program at rates of 100-150 ppm or using higher rates of 200-300 ppm as needed. Fertility can also be delivered using controlled-release fertilizers by topdressing the media surface using the medium rate listed on the product’s label, or incorporating them into the

growing medium prior to planting at a rate equivalent to 1.0-1.25 pounds of nitrogen per cubic yard of growing medium.

Physostegia are sometimes prone to iron and magnesium defi ciencies. To reduce the incidence of iron defi ciency symptoms, maintain

media pH levels between 5.5 and 6.2; if necessary, drench with acidifi ed water to bring the pH back within the desired range. If the fertilizer source does not contain adequate amounts of iron or magnesium, or if defi ciency symptoms appear, it may be benefi cial to apply magnesium sulfate or iron chelate drenches.

Considering its compact growing habit, plant height control is not usually necessary when producing physostegia ‘Crystal Peak White.’ Many growers produce them at high plant densities or at pot-to-pot con-fi gurations and still do not need to control stem elongation. If desired, spray applications of 5-ppm unicon-azole (Concise or Sumagic) or a tank mixture of 2,000 ppm daminozide (B-Nine or Dazide) + 3 ppm unicon-azole can be applied to tone the crop.

Insects and DiseasesTh ere are relatively few insects or

diseases that attack physostegia, but aphids, spider mites and Western fl ower thrips are occasionally a con-cern. Physostegia are more prone to root rot pathogens than foliar dis-eases. Th ey may also contract impa-tiens necrotic spot virus (INSV), particularly when they are overwin-tered and thrips were present during the previous summer or fall. Rou-tine scouting should be suffi cient to determine the presence of any pests

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CULTURE CONNECTIONPERENNIAL SOLUTIONS

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or diseases and to determine whether control strategies are necessary.

Forcing Although ‘Crystal Peak White’

is marketed as a fi rst-year-fl owering perennial and will bloom readily in its fi rst growing season, it is consid-ered to be a cold-benefi cial plant; providing a cold treatment (vernal-izing or overwintering them) results in more uniform fl owering and more fl owers per plant. It can be planted in the early fall, bulked up slightly and overwintered, much like a tradi-tional perennial, or planted in spring using either vernalized or unvernal-ized plugs. Provide six to 10 weeks of cold (below 41° F) when vernalizing plugs or containers of physostegia.

Physostegia are facultative long-day plants that fl ower best when they are grown under long days. Th ey also prefer to be grown under high-light intensities. If they are being grown during the late winter for early spring sales, grow them under supplemental lighting that delivers 400-500 foot-candles. For winter production, create long days using supplemental lighting for at least 16 hours per day. When the plants are being produced in the early spring (March 1 or later), they can be grown under natural light intensities with night interruption lighting to create long days.

Bloom time after long days is a

function of temperature. ‘Crystal Peak White’ fl owers in 11 to 12 weeks when grown at 68° F. Growing them cooler will increase the time to fl ower.

AvailabilityPhysostegia virginiana ‘Crystal

Peak White’ is available to the

industry as seed, plug or fi nished container. Th e seed is supplied by Benary Seed (www.benary.com) and is available through many seed distributors. Plugs can be acquired from Swift Greenhouses, Inc. (www.swiftgreenhouses.com) and several reputable plant brokers. g

Paul Pilon is a horticultural con-

sultant, owner of Perennial Solu-

tions Consulting (www.perennial-

solutions.com) and author of

Perennial Solutions: A Grower’s

Guide to Perennial Production. He

can be reached 616.366.8588 or

paul@perennial-solutions.com.

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